As noted above, it is generally used to tag a whole range of political positions associated with the same mindset that is "socially liberal." They hijacked the word which was originally meant in a context of freedom from government and liberty, using "liberal" in the sense of "permissive" and even prodigal.

In America, where freedom has strong connotations and associations with the foundation and ideals of the country (i.e. Sons of Liberty, Liberty Bell), the word liberal was more attractive and appealing than the usual labels associated with the left-wing political platforms. Tending more towards volunteer or private enterprises to do things performed by governments in Europe, names like "Socialism" were alien to Americans, and mistrusted. It was by shifting the common useage of liberal to mean socially permissive, and redefining "freedoms" and "rights" to include active benefices, rather than freedom from restrictions, that left-wing agendas were enacted. Classical liberalism and Christianity were used to justify left-wing and so-called "progressive" movements and efforts.

This sort of trojan-horse leftist strategy is typical of how most of the modern liberal agenda got enacted. For instance, conservationism started out with the stereotypically conservative types, who wanted to keep their lands looking nice, without poor people cluttering up the landscapes with their hovels and waste.